The present invention relates generally to peripheral devices, and more particularly to an apparatus and method for calibrating an image-capturing peripheral device that is associated with a document feeder.
Image-capturing peripherals such as scanners have become increasingly valuable, affordable and common devices for homes and businesses. These devices are useful for capturing and storing images such as text, graphic or pictorial images contained on documents. Various types of scanners include flatbed, drum and handheld scanners. With a flatbed scanner, one of the most common types of scanners, a document to be scanned is typically placed onto a scanning bed of the scanner, where a scanning head or sensor moves underneath the document to capture the image contained on the document. The image in digital form can then be transmitted to a connected computer, but it may instead be transmitted directly to another peripheral such as a printer or facsimile machine.
To scan a quantity of documents, an automatic document feeder, or ADF, is often combined with the scanner to feed documents. Each document can be moved past a stationary scanning head, which scans the images on the document as it passes over the scanning head, or the document can be placed on the scanning bed, where the scanning head moves relative to the document. To feed a document or documents for scanning with the document feeder, a user places the document into a tray having a pair of side guides for centering the document, although a single side alignment with a fixed edge may also be used in the tray.
Because the scanning head typically has a scan line window having a width that can be narrowed laterally and moved relative to a wider scan line width, it is desirable to adjust the lateral position of the scan line window to scan only the width of the document pages fed by the document feeder for accurate image capture. However, the side guides may not properly laterally align the document to be fed with the scan line window width of the scanning head, due to manufacturing tolerances in the document feeder. Also, because a paper path of the document feeder is typically narrower than the scanning bed width, the document feeder has room to laterally shift after assembly, contributing to the misalignment. This misalignment makes it difficult to accurately set the lateral position of the scan line window width.
To laterally align the document feeder, manual adjustments to the document feeder can be performed during assembly. A preprinted calibration sheet may be fed into the scanner, where the scanned image is compared with a stored image. Based upon the lateral offset, an operator mechanically adjusts the document feeder. However, these adjustments are labor-intensive, expensive and require tools. In addition, because the document feeder is replaceable, these manual adjustments may have to be duplicated when a document feeder is replaced or moved.
An additional method of correcting misalignment is that of calibrating the scanner via software. U.S. Pat. No. 5,813,771 to Ur et al., directed primarily to improving fill-in of digital forms, discloses a method for calibrating a printer/scanner by scanning a preprinted sheet with a document feeder to make a first image in digital form, printing the first image on a sheet using a printer to be calibrated, scanning the printed sheet to generate a second image stored in digital form, comparing the images to determine a transformation, and storing parameters of the transformation. However, this calibration method requires a costly preprinted calibration sheet and additional processing resources to transform the images, and does not adequately address lateral misalignment of the document feeder.
It would be desirable to calibrate a scanner for an associated document feeder in the field, and to adjust a scan line window width of the scanner for not only the document to be scanned but also for the document feeder, so that the scan line window scans substantially only the width of the document pages fed by the document feeder.
The improved apparatus and method of the present invention helps calibrate a peripheral device having a document feeder that feeds document pages to be scanned, and a scanning head capable of scanning at least a predetermined scan line window width that can be laterally adjusted relative to a wider scanable width. In one embodiment, the method includes the steps of feeding a target page having a target at a known location into the document feeder so that the target page can be scanned by the scanner, scanning the target on the target page, determining a calibration value for the document feeder from the lateral position of the scanned target, and adjusting the lateral position of the predetermined scan line window width using the calibration value to scan substantially only the entire width of a document to be scanned.
Preferably, the peripheral device includes or is connected to a printer. In this way the method may further include printing the target page by printing a predetermined target at a known location on a page. The target page with the printed target is then fed into the document feeder.
The predetermined target is preferably stored within firmware or software within the printer or a connected device. The known location of the target is preferably at the center of the target page, though it may also be at the edge or elsewhere on the target page.
A peripheral device is disclosed that includes a scanner function and a document feeder that feeds document pages to be scanned, and is capable of automatically adjusting the lateral position of a predetermined scan line window width so that it is substantially coextensive with the width of a document page fed by the document feeder. In one embodiment, the peripheral device includes a scanning sensor extending substantially across the width of the scanning bed capable of producing electrical signals for a multiplicity of pixels, including signals for at least a first predetermined scan line window width that is less than the scanable width of the scanning sensor, and a processor for receiving the electrical signals from the scanning sensor and producing a data file for an image scanned by the scanning sensor. The processor is configured to analyze the electrical signals received after a page has been fed for scanning, determine the lateral location of the page relative to the scanning sensor, and determine a calibration value for the document feeder from the determined lateral position of the page. The processor is further configured to use the calibration value and produce a data file by selectively using only electrical signals corresponding to the width of the scanned page.
The improved apparatus and method allows the peripheral device to be calibrated without the need for a preprinted calibration sheet, processing resources for image comparison or manual input of a calibration value. The peripheral device can be calibrated in the field after installation or adjustment of a new document feeder, with little assistance required from an operator.